1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor integrated circuit device. More particularly, the invention relates to technology that can be effectively adapted to a semiconductor integrated circuit device containing two kinds of MISFETs (metal insulator semiconductor field-effect transistors) to which different voltages are applied.
2. Prior Art
In a memory LSI such as CMOS (complementary metal oxide semiconductor) logic LSI (large scale integrated circuit) and SRAM (static random access memory) or DRAM (dynamic random access memory) and in a CMOS logic LSI mounting a memory circuit, the power source voltages may not often be the same between the internal circuit and the input/output circuit. In the CMOS logic LSI, for example, the length (gate length) of the gate electrodes of MISFETs in the internal circuit is set to be shorter than the gate length of MISFETs in the input/output circuit in order to increase the speed. In order to maintain a breakdown voltage of the semiconductor regions constituting the sources and drains of MISFETs in the internal circuit, however, the power-source voltage for the internal circuit is set to be lower than the power-source voltage for the input/output circuit. Here, in order to maintain reliability of the gate-insulating films of MISFETs in the input/output circuit having the high power-source voltage, the thickness of the gate-insulating films is selected to be larger than the thickness of the gate-insulating films of MISFETs in the internal circuit having the low power-source voltage.
Two kinds of gate-insulating films having different thicknesses are formed on a semiconductor substrate of silicon by, first, forming element isolation regions on the main surface of the semiconductor substrate and, then, subjecting the semiconductor substrate to the heat oxidation treatment of the first time to form a silicon oxide film on the surface of the semiconductor substrate. Next, active regions where the thick gate-insulating film will be formed are covered with a photoresist film, the silicon oxide film on the active regions on where the thin gate-insulating film will be formed is removed by wet etching and, then, the photoresist film is removed, followed heat-oxidizing the semiconductor substrate in the second time. That is, the thin gate-insulating film is formed through the heat oxidation of the second time, and the thick gate-insulating film is formed through the heat oxidation of the first time and through the heat oxidation of the second time.
Through their study, however, the present inventors have discovered the fact that according to the above-mentioned method of forming two kinds of gate-insulating films of different thicknesses, the active regions on where the thick gate-insulating film is to be formed is covered with the photoresist film at the time of removing, by wet etching, the silicon oxide film from the active regions on where the thin gate-insulating film is to be formed. Therefore, the thin gate-insulating film, thick gate-insulating film or these two gate-insulating films lose breakdown voltage due to contamination caused by the photoresist film and due to any damage in the step of removing the photoresist film and in the subsequent step of washing.
The object of the present invention is to provide technology capable of improving reliability of the semiconductor integrated circuit device containing a plurality of kinds of MISFETs having gate-insulating films of different thicknesses.
The above and other objects as well as novel features of the invention will become obvious from the description of the specification and the accompanying drawings.
Briefly described below are representative examples of the invention disclosed in this application.
That is, the invention is concerned with a process for forming two kinds of gate-insulating films, wherein a first insulating film is formed by etching, using a photoresist film as a mask, on a region of a semiconductor substrate on where an insulating film of a first relatively large thickness is to be formed and, then, a second insulating film is formed on the first insulating film in order to prevent the first insulating film from being scraped off in the step of washing which precedes the processing for forming an insulating film of a second relatively small thickness.
Further, the invention is concerned with a process for forming two kinds of gate-insulating films, wherein a first insulating film is formed by etching, using a photoresist film as a mask, on a region of a semiconductor substrate on where an insulating film of a first relatively large thickness is to be formed and, then, a second insulating film that has been formed in advance on the first insulating film is used as an etching stopper in the step of washing which precedes the processing for forming an insulating film of a second relatively small thickness.
Other representative examples of the invention disclosed in the application are as described below briefly.
A method of manufacturing a semiconductor integrated circuit device by forming an insulating film of a first thickness on a first active region of a semiconductor substrate and forming an insulating film of a second thickness smaller than the first thickness on a second active region is provided. This method includes the steps of:
(a) forming a first insulating film on the surface of the semiconductor substrate;
(b) forming a second insulating film which is a protection film on said the first insulating film;
(c) covering the first active region with a masking pattern;
(d) successively removing the second insulating film and the first insulating film from the second active region by using the masking pattern as a mask;
(e) selectively removing chiefly the second insulating film formed from the first active region after the masking pattern has been removed; and
(f) forming a third insulating film on the semiconductor substrate.
A method of manufacturing a semiconductor integrated circuit device by forming an insulating film of a first thickness on a first active region of a semiconductor substrate and forming an insulating film of a second thickness smaller than the first thickness on a second active region is also provided. This method includes the steps of:
(a) forming a first insulating film on the surface of the semiconductor substrate;
(b) forming a second insulating film which is a protection film on the first insulating film after the surface of the first insulating film has been removed by not more than about 1 nm;
(c) covering the first active region with a masking pattern;
(d) successively removing the second insulating film and the first insulating film from the second active region by using the masking pattern as a mask;
(e) selectively removing the second insulating film from said first active region after the masking pattern has been removed; and
(f) forming a third insulating film on the semiconductor substrate.
A method of manufacturing a semiconductor integrated circuit device is provided. This method includes the steps of:
(a) forming a first insulating film on the surface of a semiconductor substrate;
(b) forming a second insulating film which is a protection film on the first insulating film;
(c) forming a masking pattern on the semiconductor substrate so as to cover a first region on which an insulating film having a relatively large thickness will be formed but not covering a second region on which an insulating film having a relatively small thickness will be formed other than the first region;
(d) successively removing the second insulating film and the first insulating film from the second active region by using the masking pattern as a mask;
(e) after the masking pattern has been removed, removing the second insulating film by washing the semiconductor substrate, the second insulating film being used for suppressing the first insulating film from being scraped off; and
(f) forming a third insulating film on the semiconductor substrate in order to form an insulating film of a first relatively large thickness on the first region and to form an insulating film of a second relatively small thickness on the second region.
A further method of manufacturing a semiconductor integrated circuit device is provided. This method includes the steps of:
(a) forming a first insulating film on the surface of a semiconductor substrate having a first active region and a second active region;
(b) forming a second insulating film which is a protection film on the first insulating film;
(c) successively removing the second insulating film and the first insulating film from the second active region;
(d) washing the semiconductor substrate after step (c); and
(e) forming a third insulating film on the semiconductor substrate after step (d), to form an insulating film of a first relatively large thickness on the first active region and to form an insulating film of a second relatively small thickness on the second active region;
wherein in effecting the washing in step (d), the rate for etching the second insulating film is larger than the rate for etching the first insulating film, and the second insulating film is removed from the second active region.
Another method of manufacturing a semiconductor integrated circuit device is provided. This method includes the steps of:
(a) forming a first insulating film on the surface of a semiconductor substrate;
(b) forming a second insulating film which is a protection film on the first insulating film;
(c) forming a masking pattern on the semiconductor substrate so as to cover a first region on which an insulating film having a relatively large thickness will be formed but not covering a second region on which an insulating film having a relatively small thickness will be formed other than the first region;
(d) successively removing the second insulating film and the first insulating film from the second active region by using the masking pattern as a mask;
(e) after the masking pattern has been removed, washing the semiconductor substrate using the second insulating film as a stopper; and
(f) forming a third insulating film on the semiconductor substrate in order to form an insulating film of a first relatively large thickness on the first region and to form an insulating film of a second relatively small thickness on the second region.
In forming a plurality of kinds of gate insulating films having different thicknesses according to the above-mentioned means, the photoresist pattern is not directly formed on the first insulating film that constitutes a relatively thick gate-insulating film but, instead, the photoresist pattern is formed via the second insulating film or via a reformed layer of the first insulating film. Therefore, contaminants from the photoresist film adhere on the second insulating film or on the reformed layer of the first insulating film. As the first insulating film, there is used a film formed by heat-treating the semiconductor substrate, a film formed by the chemical vapor-phase deposition method, or a film formed by nitriding the film that has been formed by the chemical vapor-phase deposition method. As the second insulating film, there is used a film formed by, for example, the chemical vapor-phase deposition method which is different from the method of forming the first insulating film. This enables the second insulating film in the washing solution to be etched at a rate larger than the rate of etching the first insulating film. By selectively removing the second insulating film by utilizing the difference in the etching rate, therefore, the first insulating film is not affected by the contamination caused the resist and, besides, damage to the first insulating film can be avoided in the step of removing the resist and in the subsequent washing step. By removing the surface portion of the first insulating film within such a degree that no defect develops in the film, further, it is allowed to remove contaminants adhered on the interface between the first insulating film and the second insulating film, contributing to further improving reliability of the gate-insulating film.
According to the above means, further, in effecting the washing prior to forming the insulating film of the relatively small second thickness, the second insulating film prevents the first insulating film from being scraped off on the region on where the insulating film of the relatively large first thickness is formed, so that weak spots in the first insulating film will not be exposed and that fine pores will not be formed. Therefore, the gate-insulating film having the relatively large first thickness is suppressed or prevented from losing breakdown voltage, and the quality of the gate-insulating film can be improved.
According to the above means, further, in effecting the washing prior to forming the insulating film of the relatively small second thickness, the second insulating film formed in advance on the first insulating film on the region on where the insulating film of the relatively large first thickness has been formed, works as an etching stopper so that the first insulating film is not scraped off, weak spots in the first insulating film will not be exposed and that fine pores will not be formed. Therefore, the gate-insulating film having the relatively large first thickness is prevented from losing the breakdown voltage that stems when the first insulating film is scraped off during the washing, and improved quality of the gate-insulating film can be maintained.